A sheet processing device that performs specified post-processing on a sheet (paper sheet) conveyed from an image forming apparatus is known. The sheet processing device is provided with a sheet binding mechanism. The sheet binding mechanism may include a stapler which staples the sheets together with a staple or a crimping mechanism which processes a sheet into a tooth or detent shape by pressure to temporarily fix a plurality of such sheets together. After being processed by the stapler or the crimping mechanism, holes from the staple or a tooth or detent shape is left in the sheet and thus the stapler or the crimping mechanism limits the ability to reuse the sheet. In recent years, a method for binding a sheet using an adhesive tape has been considered. However, when a plurality of sheet (bundles) having been adhered together by tape are stacked, the resulting stack of bundles of sheets is influenced by the thickness of the tape. That is, when a plurality of bundles of sheets subjected to tape binding processing are stacked one over the other, the stack height of the stacked bundles is partially increased in the periphery thereof where the tape binding portion is present. When the stacked height of bundles of sheets is excessively increased where the tape binding portions are present, the balance of the stack of bound bundles of sheets may be deteriorated or the stack of bundles of sheets may collapse and drop. Additionally, when the adhesive tapes of adjacent bundles in a stack come into contact with each other, the adhesive layers of the adhesive tape of the respective adjacent bundles may have the adhesive layers thereof adhered to each other. When the adhesive layers of the adhesive tape of adjacent bundles of sheets become adhered to each other, a plurality of bundles of sheets stacked on each other may be adhered to each other and each bundle of sheets will become hard to handle individually.